Carbon fibers are currently generally produced from carbon precursors comprising non-renewable fossil sources, such as coal, oil, and natural gas, using time-consuming, energy-intensive, and expensive processes. Such carbon fibers are utilized in engineering applications, such as reinforcement of polymer materials and carbon-carbon composites, where properties such as high tensile strength and/or modulus are key prerequisites, notably in aerospace applications of carbon fibers. However, such engineering properties are not required for applications of the activated form of the carbon fibers; indeed, the engineering properties are essentially destroyed during the process of making the activated form of the carbon fibers.
Activated carbon fibers (ACFs) are generally produced from carbon fibers through a high-temperature carbon gasification process which proceeds in an oxidizing atmosphere, such as carbon dioxide or steam. This process burns away carbon to create high surface area and pore volume in the activated form of the fiber, but in the process decreases product yield and thus further enhances production cost. Given that the major part of the cost of producing a carbon fiber for engineering applications is associated with the creation of those engineering properties, the cost of the activated form of the carbon fibers is inflated by the processing steps to create the unnecessary engineering properties, which results in an overall cost of ACFs that is generally too high for all but a few high-value, niche applications. Moreover, because conventional ACF products are produced from conventional carbon fibers through a high-temperature carbon gasification process, the chemical composition of the ACF is dependent on, and therefore limited by, the composition of the original carbon precursor.
Although uncommon, some references disclose production of ACFs from lignin or lignocellulosic materials. JP 2002038334 entitled “Method for producing fine activated carbon fiber and fine activated carbon fiber produced thereby” discloses a method for producing an ACF containing a step to prepare a dissolved or molten polymer material obtained by dissolving or melting a pyranose-ring or lignin-based polymer material, a step to spin the dissolved or molten polymer material and obtain a fiber of the dissolved or molten polymer material having an average fiber diameter of <=3 μm, a step to produce a fine carbonized fiber derived from the pyranose-ring or lignin-based polymer material by the heat-treatment of the fiber and a step to activate the fine carbonized fiber to obtain the ACF. JP 57118376 entitled “Zinc-halogen battery” discloses using various materials, such as cellulose series fiber, acrylic series fiber, lignin series fiber, special pitch of petroleum series, vinylon series fiber, etc. and processing these materials by burning into carbonized fiber, or they are further heat treated at a high temperature to get carbon fiber. This carbon fiber is used as an electrode in a woven fabric, a non woven fabric, or a felt like shape formed under pressure, being cut in desired electrode shapes. The electrode is processed by dipping in concentrated nitric acid or electrolyzing in a halogen aqueous solution, then the surfaces of carbon fiber are activated. The term “activated” is used in the context of surface-treating the carbon fiber fabric formed from the carbon fibers to obtain a suitable electrode material for zinc-halogen batteries; not in the context of producing porous, high surface area ACFs for adsorptive applications. The agent (HNO3) used to “activate” the carbon fiber cannot create the characteristics desired of “activated carbon fibers”, nor is it a chemical activation agent that is suitable for producing activated carbon products.